QMatrix4x4 and OpenGL

[NorskQt]

Hi,

I have two simple questions related to QMatrix4x4 :

1. Is this matrix OpenGL compliant? If not, is there an easy way converting it to OpenGL matrix (float array of dimesion 16)?
2. How is this matrix indexed, usual C/C++ notation starting from zero, eg Qmatrix4x4 m(0,0) = refers to the first element in the matrix row : 0 and column : 0)?

Thanks!

[Immii]

QMatrix4x4 is transformation matrix in 3D space so you can use it where ever you want.

[NorskQt]

Immii,

You sound like you have not been working with 3D graphics.

Any qualified answer, please?

Thanks.

[dangelog]

[quote author="NorskQt" date="1293299650"]Hi,

I have two simple questions related to QMatrix4x4 :

1. Is this matrix OpenGL compliant? If not, is there an easy way converting it to OpenGL matrix (float array of dimesion 16)?
2. How is this matrix indexed, usual C/C++ notation starting from zero, eg Qmatrix4x4 m(0,0) = refers to the first element in the matrix row : 0 and column : 0)?

Thanks![/quote]

Unfortunately, QMatrix4x4 is a matrix of 16 qreals, which may or may not be GL_FLOAT -- and usually they are not, since qreal is double everywhere except on ARM, and GL_FLOAT is float everywhere. Qt uses some internal macros to do the job: see for instance
http://qt.gitorious.com/qt/qt/blobs/master/src/opengl/qglshaderprogram.cpp#line2188

Apart from this, internally QMatrix4x4 is a qreal[ 4 ][ 4 ] packed in column-major order (i.e. operator()(x, y) will assign to data[y][x], matching OpenGL), so the first element is indeed (0, 0).

[NorskQt]

Hi Peppe,

Thank you very much for providing information about QMatrix4x4. It's a kind of strange though because Qt works with OpenGL and Qt's 3D-graphics matrix is not OpenGL compliant. This is something that the Qt developers should consider.

Thank you very much again.

[bbuerger]

Hi there,

correct my if I'm wrong but opengl can be used with floats.
Just use gl...d instead of the gl...f in these case glLoadMatrixd

Greetings,
bbuerger